What’s the difference between an air source and ground source heat pump?

what are the pros and cons of air source heat pumps
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    If you are considering a renewable energy heating system for your home or business, a heat pump is an excellent choice. The most common types of heat pumps are air source and ground source. Both are low-carbon heating solutions and can reduce energy costs. Both can produce hot water and warmth via underfloor heating or a central heating system and become cooling systems in warmer weather.

    So what’s the difference, and which one is best for your needs? Both heat pumps work on the same basis, but the main difference is that they gather and transfer heat from different sources.

    An air source heat pump extracts heat from the outdoor air and requires a modest-sized outside unit. A ground source heat pump draws heat from the earth via underground loops and is slightly more energy efficient, but needs a large outdoor space and is more expensive to install.

    It’s important to consider the pros and cons of air source vs ground source heat pumps and get advice from a certified heating specialist like Cinergi. We can make a thorough assessment of your property and make recommendations for the most efficient and cost-effective solution.

    Contact us today to ask us a question or request a quote. In the meantime, read on for our useful guide on the difference between air and ground source heat pumps.

    How does a heat pump work?

    An air source heat pump works by absorbing heat energy from the outdoor air using refrigerant-filled coils. This heat is then compressed to a higher temperature and transferred indoors via a heat exchanger, where it warms the indoor space. Read more on air source heat pumps here.

    A ground source heat pump takes energy from the earth via a ground loop, which is a system of underground pipes filled with a heat transfer fluid. The loops can be installed in horizontal runs (trenches) or boreholes (if space is limited) and require significant groundwork.

    The fluid absorbs heat from the ground and carries it to an indoor heat pump. The heat pump then increases the temperature of the fluid further and distributes it throughout the building to heat water and rooms. Read more on ground source heat pumps here.

    How do I know which heat pump to choose?

    There are several key factors that you should consider when choosing between a ground source and air source heat pump:

    Upfront cost

    Air source heat pumps generally have lower installation costs compared to ground source heating systems. An air source heat pump uses simpler technology and requires less labour-intensive groundwork, meaning they are cheaper to install. Ground source heat pumps are more expensive to install due to the excavation required for ground loops.

    Carbon emissions

    Traditional heating systems use harmful fossil fuels, so a move to any type of renewable heating system is more environmentally friendly. Both air source pumps and ground source pumps can significantly reduce your household or business carbon emissions.

    Ground source heat pumps do have slightly lower carbon emissions compared to air source heat pumps, however. That’s because ground temperatures are more stable than air temperatures (particularly in the chilly old UK), which means that they operate at higher efficiency levels and, therefore, use less electrical energy.

    According to the Energy Saving Trust, as of January 2024, a three-bedroom property upgrading to an air source heat pump from an old gas boiler can save 2,900kg of CO2 per year, and 4,500 kg with a ground source heat pump.

    Efficiency

    The efficiency of a heat pump is measured by the coefficient of performance (COP), which represents the ratio of heat output to electricity input. The latest air source heat pumps achieve COP values ranging from 2.5 to 4 or even higher, meaning they can produce 2.5 to 4 times more heat energy than the electricity they consume. However, this can be reduced when the inlet temperature drops, so they use more electricity in colder weather.

    Ground source heat pumps are not affected by fluctuations in outdoor temperatures, so generally have higher COP values of 3 to 5 or higher, making them more energy-efficient and cost-effective over the long term.

    Property size

    An air source pump has a maximum output of around 16.5kW, which is enough for a typical five-bed property (based on a standard 100amp single-phase electricity supply). For two to three-bedroom homes, a smaller heat pump will suffice.

    Ground source systems have a maximum output of around 24kW, making them a better solution for larger properties. At Cinergi, our experience is that if your property requires less than 16.5kW to heat, an air source heat pump is likely the most suitable and cost-effective option. Of course, there are exceptions to this rule, and we thoroughly assess each property before making our recommendations.

    Maintenance and running costs

    Heat pumps are much more cost-effective than more traditional heating systems as they rely on electrical energy rather than fossil fuels. Over time, you can expect a significant difference in your energy bills.

    According to the Energy Saving Trust, as of January 2024, this could be as much as a £340 saving per year for a three-bedroom home when upgrading to an air source heat pump from an old gas boiler. Visit the Energy Saving Trust website.

    Both types of heat pumps require little maintenance and have life spans of at least 20 years, resulting in much cheaper running costs than gas boilers. The pipes in a ground loop system are expected to last up to 50 years, meaning there is no need to dig up your garden quite so soon!

    Outdoor space

    How much space you have is another key factor when deciding between an air source or ground source pump. An outdoor air source heat pump unit is typically no larger than 1.5m wide and 1.5m tall, making it suitable for most properties. They can even be installed on roofs.

    The size of a ground source heat pump depends on the property’s energy requirements and whether you opt for a vertical or horizontal system. But you need a large outdoor space for the ground array, typically between 700 and 1,200 square metres

    Aesthetic

    How the system looks is naturally a concern for homeowners. While a ground source heat pump is tucked out of sight, an air source heat pump requires an outdoor unit. These can be discreetly placed and there are plenty of ways to make them look aesthetically pleasing, as detailed in this article on.

    While we’re on aesthetics, let’s address noise; contrary to popular belief, an air source heat pump doesn’t have a particularly high noise output. They make no more than 60 decibels, which is the same as a microwave. A ground source unit, on the other hand, doesn’t need a fan, so is silent. This may make a difference to the more noise-sensitive among us!

    Air source heat pumps vs ground source heat pumps

    Both ground and air source heat pumps are highly efficient and an environmentally friendly alternative to fossil fuels. They work in the same way, delivering heating, cooling and hot water. Also, both are eligible for a £7,500 grant from the Boiler Upgrade Scheme. But considering the differences between the two, let’s summarise the pros and cons of air vs ground source.

    Air source heat pumps

    ProsCons
    Cheaper to installNeeds an external unit (which is not pretty but can be disguised in numerous ways)
    Easier and quicker installation processMore noisy than a ground source heat pump
    Requires little space outdoorsLess efficient than ground source heat pumps in cold air, making it suitable for more moderate climates

    Ground source heat pumps

    ProsCons
    Slightly more efficient than an air source heat pump overall, especially when the air temperature dropsHigher installation costs
    No ‘unsightly’ external unit neededNeed a much larger space than air source
    No noise

    Looking for heat pump advice? Get in touch with Cinergi

    Cinergi is one the leading installers of heat pumps in Hampshire, West Sussex, Wiltshire, Dorset and Somerset. Our friendly, family-run team are all MCS-accredited installers and can offer impartial advice on which system is right for your property. Please get in touch to request a quotation.

    FAQs – what’s the difference between an air source and a ground source heat pump?

    Can you use both an air source heat pump and a ground source heat pump to supply energy to your home?

    Having multiple heat pumps is possible and can be advantageous when the temperature drops. A heat pump can also be integrated with a traditional boiler. Hybrid systems require a lot of technical expertise, so if you are considering this option, choose a highly accredited installer like Cinergi.

    What grants are available for heat pumps?

    The Renewable Heat Incentive Scheme has been replaced by the Boiler Upgrade Scheme, which provides £7,500 towards the cost of air source and ground source heat pumps to eligible property owners. The Boiler Upgrade scheme also provides £5,000 towards biomass boilers. See this article on air source heat pump grants for further details.

    How much can a heat pump save me?

    A heat pump unit runs on electricity, so is generally cheaper to run than a gas boiler. Take a look at the Energy Saving Trust website to find out how much you can save, which is as much as £1,100 per year when replacing old electric storage heating with an air source heat pump (January 2024).

    Picture of Dan Loveridge
    Dan Loveridge

    Dan is the managing director at Cinergi, a renewable energy company based in southern England specialising in air source heat pumps and EV charging solutions.

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